have been either accreted from the
primordial protoplanetary disk (as with
giant planets), or appeared as secondary atmospheres created from outgassing or collisions with other bodies after the planets formed.
Over the last few years, our group has
started exploring exoplanet atmospheres by making differential spectroscopic observations of exoplanets
passing in front of their host suns (see
details on this technique starting on
page 9). These ground-based transit
observations yield spectra (and thus
clues to the composition of exoplanet
atmospheres) with precisions that rival
those taken with space telescopes.
Using GMOS to Probe
WASP-12b: A Hot Exoplanet
Prototype
One exoplanet that has long fascinated
us is WASP-12b. This hot, Jupiter-sized
planet orbits its Sun-like (G0) parent
star every 26 hours. Recent work has
suggested that this highly-irradiated
exoplanet could have a carbon-to-oxygen ratio (C/O > 1) that is significantly
higher than that of the Sun (0.54, Madhusudhan et al., 2011). When a planetary atmosphere is so carbon-rich,
different chemical pathways dominate
and unexpected molecules, such as
methane and metal hydrides, begin to
emerge.
To better understand the atmospheric
composition of WASP-12b (Stevenson et
al., 2013) we used the Gemini Multi-Object
Spectrograph on the Gemini North telescope (GMOS-N) on Mauna Kea to perform
the transit spectroscopy technique described starting on page 8.
October2013
Figure 1.
“White” light curves for the hot Jupiter-type exoplanet WASP-12b
Panel A: Transit time series, from January 25, 2012, after correcting
for telluric effects using the simultaneously observed reference star
(points). The data exhibit an unexpected instrument systematic that
is modeled using an analytic function (black line). The combined
transit and instrument model is shown as the blue line. Panel B:
Same as panel A, but for the January 26th observation. Panel C:
White light curves for both nights with the instrument systematic
removed (points). The combined transit model is shown as the black
line. The residuals have a root mean square of 180 parts per million.
GeminiFocus
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